A tunable reentrant resonator with transverse orientation of electric field for in vivo EPR spectroscopy

There has been a need for development of microwave resonator designs optimi zed to provide high sensitivity and high stability for EPR spectroscopy and imaging measurements of in vivo systems. The design and construction of a novel reentrant resonator with transversely oriented electric field (TERR) and rectangular sample opening cross section for EPR spectroscopy and imagi ng of in vivo biological samples, such as the whole body of mice and rats, is described. This design with its transversely oriented capacitive element enables wide and simple setting of the center frequency by trimming the di mensions of the capacitive plate over the range 100-900 MHz with unloaded Q values of approximately 1100 at 750 MHz, while the mechanical adjustment m echanism allows smooth continuous frequency tuning in the range +/-50 MHz. This orientation of the capacitive element limits the electric field based loss of resonator Q observed with large lossy samples, and it facilitates t he use of capacitive coupling. Both microwave performance data and EPR meas urements of aqueous samples demonstrate high sensitivity and stability of t he design, which make it well suited for in vivo applications. (C) 1999 Aca demic Press.